The present invention relates to a process for the alkylation of aromatic amines, particularly the ortho-alkylation of aromatic diamines.
Processes for the preparation of orthoalkylated aromatic amines from alkenes are known in the art. In one process, aluminum is dissolved in aniline to form aluminum anilide which serves as a catalyst for the alkylation of the aniline or of other aromatic amines. Such a process is taught in U.S. Pat. No. 3,649,693 to Napolitano. Napolitano teaches that the alkylation itself is conducted at significantly elevated temperatures and pressures. Various other references have taught that the addition of mercury chloride, various Friedel Crafts catalysts, iodine or iodine compounds are helpful in improving the efficiency of the reaction.
U.S. Pat. No. 4,760,185 to Becker teaches heating a diamine with an aluminum/zinc alloy and aluminum chloride in the absence of aniline until the evolution of hydrogen is complete. This catalyst mixture is then reacted with a lower alkene at significantly elevated pressure and temperature to form the alkylated phenylenediamine.
The methods known for the ortho-alkylation of aromatic diamines require substantially elevated reaction pressures and temperatures; require the presence of environmentally questionable substances such as mercury chloride; require expensive catalysts or require some combination of these factors. Thus what is needed is a method for the ortho-alkylation of aromatic amines which utilizes less expensive, less toxic catalysts and which utilizes relatively mild alkylation conditions.